Direct positive photographs using aerial fogging developer



Feb. 21, 1950 e. E. FALLESEN 2,497,875

DIRECT POSITIVE PHOTOGRAPHS USING AERIAL FOGGING DEVELOPER Filed Oct.17,1947

LOG E 5% 3- f! "v v ILL ISA/3U GEORGE E .FALLESEN INVENTOR h. h. Pmm' ATTORNEYS I Patented Feb. 21, 1950 DIRECT POSITIVE PHOTOGRAPHS USINGAERIAL FOGGING DEVELOPER George Earle Fallesen, Rochester, N. Y.,assignor to Eastman Kodak Company, Rochester, N. Y., a corporation ofNew Jersey Application October 17, 1947, Serial No. 780,405

3 Claims.

ticularly to a method of making direct positive photographs.

Direct positive effects may be produced by solarizing the developablelatent image by overexposure, by using a second exposure to obtain theSabattier or the Clayden effect or by redeveloping a developed negativeimage. Solarizable sensitized products require very intense exposures toobtain the desired direct positive photograph. The use of a secondexposure has obvious disadvantages from the point of viewof practicaltechnique. Redevelopment adds at least two operations to the usual andnormal developing procedure.

It is therefore an object of the present invention to provide a novelmethod for obtaining direct positive photographs. A further object is toprovide a method for obtaining direct positive photographs which doesnot require solarization, a second exposure or a redevelopment. A stillfurther object is to provide a method for obtaining direct positivephotographs which avoids the disadvantages of the prior art methods ofobtaining such photographs. An additional object is to provide a methodfor obtaining direct positive photographs which does not require exof myinvention is a gelatino-silver halide emulsion such as a silver bromideemulsion, a silver bromoiodide emulsion or a silver chloroiodideemulsion. It need not contain optical sensitizing dyes although certainsensitizing dyes may .be added to it for the purpose of inducing aerialThe digestion should be carried out without the use of sulfursensitizers. An emulsion of this type is that known as Burtons emulsion,described in Wall, Photographic Emulsions. 1929, pages 52 and 53.Burtons emulsion is made as follows:

A. Silver nitrate grams 100 Water "cubic centimeters 500 Ammoniarto formclear solution.

B. Potassium bromide "grams" 80 Potassium iodide cl0 50 Soft gelatin"do-.." 20

W Water cubic centimeters 1000 C. Dry gelatine grams 250 2 B is heatedto C. and A, cold, added to B with constant shaking, digested for 20minutes at 50 C., and allowed to cool slowly. C is added after beingallowed to swell for 20 minutes in water, drained and melted. Theemulsion is then set and washed.

An internal latent image emulsion, that is, one which forms the latentimage mostly inside the silver halide grains, as described on pages 296and 297 of Mees The Theory of the Photographic Process, 1942, isespecially useful for the process of my invention.

Most of the internal latent image emulsions are silver bromo-iodideemulsions of high iodide content, preferably containing at least 10%-20%of iodide. Burtons emulsion is an emulsion of this type, having a silveriodide content of approximately 40% of the content of silver halide. Itis not absolutely essential, however, for the emulsion to contain silveriodide.

An internal latent image emulsion made as described in Davey and KnottU. S. application .Serial No. 790,232 filed December 6, 1947, now

abandoned, may also be used according to my invention. This emulsion isprepared by first forming in the absence of ammonia and in one or morestages silver salt grains consisting at least partly of a silver saltwhich is more soluble in water than silver bromide, subsequentlyconverting the grains to silver bromide or silver bromoiodide and if thesilver iodide content of the emulsion is less than 6% calculated on thetotal silver halide, treating such grains with an iodine compound tobring the silver iodide up to at least 6%, ripening preferably in theabsence of ammonia and then either washing out some of the soluble saltsor washing out the whole of the soluble salts, followed by the additionof soluble salts such as soluble chloride or bromide. An example of anemulsion made in this way is as follows:

Solution No. l:

Inert gelatine 20 grams K01 20 grams at 40 0. Water 560 cubiccentimeters solllltziili No. 2:

grams 0 Water 520 cubic centimeters} 45 soluiionrgl'o. 3:

gr 3 195 grams a Water. 520 cubic centimeters at 45 Solution N KBr-.-grams KL i. 40 grams at 45 0. Water 500 cubic centimeters of 10%solution of KCl (by weight), and then add water to make .3 litres.

An internal latent image type of silver halide emulsion may be definedas one which, when a test portion is exposed to a light intensity scalefor a fixed time between /100 and 1 second, and developed for 4 minutesat 20 C. in the ordinary, surface developer (Example 1), exhibits amaximum density not greater than /5 the maximum density obtained whenthe same emulsion is equally exposed and developed for 3 minutes at 20C. in an internal type developer (Example 2). Preferably the maximumdensity obtained with the surface developer is not greater than t; themaximum density obtained when the same emulsion is developed in theinternal type developer. Stated conversely, an internal la tent imageemulsion, when developed in an internal type developer (Example 2)exhibits a maximum density at least 5, and preferably at least 10, timesthe maximum density obtained when the same emulsion is exposed in thesame way and developed in a surface developer (Example 1).

The developer used according to my invention should be one whichproduces oxidation fog or aerial fog. Such developers have beendescribed by Dundon and Crabtree in American Photo,,- raphy, 1924, vol.18, page 742. An example of such a developer is a, hydroquinonedeveloper containing little or no sulfite, and is illustrated in Example3.

My new process is based on the production of fog in the unexposed areasof the emulsion and the inhibition of development in the exposed areas.With the emulsions heretofore described and with developers referred toin the preceding paragraph, this action occurs in the following way. Theemulsion is exposed in the usual manner and is developed in such a waythat aerial fog is produced. The unexposed silver halide grains arethoroughly and ,efifectively .fogged; at the same time, the developmentin the areas containing the latent image is so restrained that a verylow density is obtained in the area of greatest exposure. The inhibitionof fogging in the regions containing a latent image is proportional tothe exposure, the least density being obtained in the region of greatestexposure. In this Way, a reflection density of 0.02 has been measured onpaper in the region of greatest exposure and a fog density of more than1.5 has been measured in the regions of no exposure.

The aerial fog is produced according to my invention in various ways andmay be accelerated or intensified by resorting to various expedients.The developer used should preferably have low sulfite content and shouldcontain no silver halide solvent more powerful (as a silver halidesolvent) than sulfite. developer having low sulfite concentration isespecially adapted to the production of aerial fog. A developer of thistype is illustrated in Example 3. Aerial fog may also be increased bybubbling air vigorously through the developer in such manner that theair comes frequently into contact with the emulsion surface of thephotograph during development. Certain chemical agents such as coppersulfate incorporated either in the developer or in the emulsion itselfmay be used to produce or encourage the production of aerial fog.Hydrogen peroxide or certain dyes, such as methylene blue, increaseaerial fog.

In addition to the use of a developing solution which produces aerialfog, the emulsion may As stated above, a hydroquinone' dition to it ofcertain compounds.

' U. S. Patents 1,846,301 and 2,058,406) may be incorporated in theemulsion. Other compounds such as the quaternary salt,benzothiazolemethiodide, also increase the susceptibility of theemulsion to aerial fog, as do silver iodide and potassium iodide.

Fogging agents containing labile sulfur are generally unsuitable for useaccording to my invention. The fogging action should produce developablesurface latent image in the unexposed silver halide grains.

An ordinary, surface type developer, that is, one which develops animage only on the surface of the grains of an internal latent imageemulsion, is the following:

EmampleI p-Hydroxyphenylglycine "grams" 10 Sodium carbonate (crystals)do Water to 1iters 1 Development time, 4 min. at 20 C.

An internal type developer, that is, one which develops an image insidethe grains of an internal latent image emulsion, is the following:

Example 2 Hydroquinone grams l5 Monomethyl-p-aminophenol .sulfate do 15Sodium sulfite (anhydrous) do .50 Potassium bromide do 10 Sodiumhydroxide do 25 Sodium thiosulfate (crystals) do- 20 Water to liters 1Development time, 3 min. at 20 C.

Example 3 I-Iydroquinone grams- 22.5 Sodium sulfite do 30Paraformaldehyde do 7.5 Potassium metabisulfite do 2.6 Boric acid,crystals do 7.5 Potassium bromide do 1.6 Water to make liters 1.0

The developer was agitated durin the development by bubbling air throughit so that the air came in contact with the emulsion. The emulsion wasthen fixed in hypo and washed. The resulting sensitometric curve wasmeasured and plotted as in the accompanying drawing, in which increasingexposures are plotted as ordinates and density is plotted as theabscissa. It is apparent that a positive image having suitablecharacteristics was obtained as indicated by the slope and position ofthe curve.

It will be evident to those skilled in the art that my process aifords ameans for obtaining a direct positive photograph by a simple exposureand development technique and therefore avoids the necessity of highintensity exposures or a second exposure or redevelopment in order toobtain a direct positive image. Y Y

I claim:

1. The method of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time between/100 and 1 second and development for 3 minutes at 20 C. in thefollowing internal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydroussodium sulfite 50 Potassium bromide Sodium hydroxide 25 Sodiumthiosulfate 20 gives a maximum density at least 5 times the maximumdensity obtained when the equally exposed silver halide emulsion isdeveloped for 4 minutes at 20 C. in the following surface developer (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 literand developing only the unexposed portion of said emulsion layer in anaerial fogging developer with access of oxygen.

2. The method of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time between/100 and 1 second and development for 3 minutes at 20 C. in thefollowing internal type developer:

Grams Hydroquinone Monomethyl-p-aminophenol sulfate 15 Anhydrous sodiumsulfite 50 Potassium bromide 10 Sodium hyd'pxide 25 Sodium thiosulfateWater to 1 liter gives a maximum density at least 5 times the maximumdensity obtained when the equally exposed silver halide emulsion isdeveloped for 4 minutes at 20 C. in the following surface developer (I)Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 literrendering only the unexposed silver halide grains of said layerdevelopable in the following developing solution with access of oxygen:

Grams Hydroquinone 22.5 Sodium sulfite 30 p-Formaldehyde 7.5 Potassiummetabisulfite 2.6 Boric acid (crystals) 7.5 Potassium bromide 1.6

Water to 1 liter 6 and developing said grains to metallic silver in thesame solution in which they were rendered developable.

3. The method of obtaining a direct positive image in a silver halideemulsion layer, which comprises exposing to light rays to which theemulsion is sensitive, a silver halide emulsion layer a test portion ofwhich upon exposure to a light intensity scale for a fixed time betweenand 1 second'and development for 3 minutes at 20 C. in the followinginternal type developer:

Grams Hydroquinone 15 Monomethyl-p-aminophenol sulfate 15 Anhydroussodium sulfite 50 Potassium bromide 10 Sodium hydroxide 25 Sodiumthiosulfate 20 Water to 1 liter gives a maximum density at least 5 timesthe maximum density obtained when the equally exposed silver halideemulsion is developed for 4 minutes at 20 C. in the following surfacedeveloper (I):

Grams p-Hydroxyphenylglycine 10 Sodium carbonate 100 Water to 1 literand immediately immersing said layer in a develoninsolution o subtantiallv t e following composition with air bubbling through it incontact with said emulsion:

Grams Hydroquinone 22.5 Sodium sulfite 30 p-Formaldehyde 7.5 Potassiummetabisulfite 2.6 Boric acid (crystals) 7.5 Potassium bromide 1.6

Water to 1 liter to develop metallic silver in the unexposed portions ofsaid layer.

GEORGE EARLE FALLESEN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Crouse et al May 28, 1946 OTHERREFERENCES Wall, Photographic Emulsions, Publ. 1929 by Amer. Phot. Publ.00., Boston, pages 52 and 53.

Clerc, Photography, Theory and Practice," Pub. 1937 by Sir Issac Pitman& Sons, Ltd., New York, page 229.

Number

1. THE METHOD OF OBTAINING A DIRECT POSITIVE IMAGE IN A SILVER HALIDEEMULSION LAYER, WHICH COMPRISES EXPOSING TO LIGHT RAYS TO WHICH THEEMULSION IS SENSITIVE, A SILVER HALIDE EMULSION LAYER A TEST PORTION OFWHICH UPON EXPOSURE TO A LIGHT INTENSITY SCALE FOR A FIXED TIME BETWEEN1/100 AND 1 SECOND AND DEVELOPMENT FOR 3 MINUTES AT 20*C. IN THEFOLLOWING INTERNAL TYPE DEVELOPER: